Biochem Chapter 11

Biochem Chapter 11 - Chapter 11 DNA Replication and...

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Unformatted text preview: Chapter 11 DNA Replication and Transcription: Biosynthesis of DNA and RNA Dr. J Davis - Concepts in Biochemistry - 3rd Edition Chapter Seven Chapter 11 Homework #4-6, 10, 11, 13, 14, 18, 21, 24, 25, and 35 3 Chapter Outline 11.1 Replication of DNA 11.2 Action of DNA Polymerases 11.3 DNA Damage and Repair 11.4 Synthesis of RNA 11.5 Post-transcriptional Modification of RNA 11.6 Base Sequences in DNA 4 11.1 Replication of DNA 11.1 REPLICATION OF DNA Recall: We now know DNA has a dynamic structure that includes at least 3 types of DNA 2 o structure (A, B, & Z DNA) and extensive 3 o structure [Supercoiling, primarily in prokaryotes]. During Replication/transcription, DNAs double helix is unwound into single strands, and bent into forks for decoding. The replication process must be accurate, precise, gentle and rigorously controlled to prevent any changes in the DNA primary structure which leads to errors in the transfer of genetic information to the next cell generation. All the steps must be executed with great care/ accuracy to avoid errors . Most information we have regarding DNA replication comes from data from prokaryotic cells [E. coli]. Our knowledge of processes occurring in Eukaryotic cells is incomplete. 5 11.1 Replication of DNA Characteristics of The DNA Replication Process 1. DNA replication is Semiconservative! This was proven in some extraordinary experiments at Harvard [1957] using radioactive 15 Nitrogen to label DNA in growing E coli cells. Cells 1 st grown for several generations in the 15 N-labeled DNA, but were later transferred into fresh media with unlabeled nitrogen 14 N. Next: the new DNA formed was isolated using density gradient centrifugation to separate, identify, and characterize the expected 3 kinds of DNA. 6 Figure 11.1 Two possible Models of DNA Replication Figure 11.1 Two possible Models of DNA Replication 7 Fig 11.2 Fig 11.2 Density Gradient Centrifugation Density Gradient Centrifugation 8 9- The results confirmed that the replication process occurs via semi-conservative mechanisms. 10 Replication Factoid: Consider: DNA (the human genome) consists of 3 billion base pairs. DNA in each cell must be replicated with minimal error. Error rates are as low as ~ 1/10 billion to ~1/100 billion bases. It takes several hours to replicate all the DNA . 11 11.1 Replication of DNA Characteristics of The DNA Replication Process (2) 2. Replication begins at Discrete Points on DNA J Cairns (late 50s): was 1 st to show (visually) that ds-DNA is replicated at structures aka replication forks. He used 3 H-Thymidine to label cells and used autoradiography to actually see these forks. With E. coli (circular) DNA molecules, he observed two discrete replication start points [aka Origins] which proceeded in both directions, thereby copying each strand (Fig. 11.4)....
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Biochem Chapter 11 - Chapter 11 DNA Replication and...

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